In recent years, there has been a remarkable spread of digital equipments with an image input function such as a digital still camera, a digital video camera, a mobile phone with a camera and a personal digital assistant (PDA: Personal Digital Assistant) with a camera, and increase of the number of pixels and enhancement of performance of an image pickup element to be mounted on those equipments, have been advancing rapidly. Therefore, in order to take full advantage of the performance of an image pickup element with increased number of pixels, high optical performance is required also for an image pickup optical system which guides an optical image of a subject onto an image pickup element. Further, since portability is required in the above digital equipments, small-sizing of the equipments is also needed.
As a way to small-sizing a digital equipment, it can be considered to make an image pickup optical system compact. As a way to making an image pickup optical system compact, there has been conventionally known a reflection prism. For example, Patent Literature 1 proposes a structure that one reflection prism for bending an optical path is arranged in an optical path of an image pickup optical system. Further, Patent Literature 2 proposes a structure that two reflection prisms for bending an optical path is arranged in an optical path of an image pickup optical system.